Grease composition



United States Patent 3,269,945 GREASE COMPOSITION John F. Hedenburg, Cheswick, and Chester S. Tempalski,

Pittsburgh, Pa., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Filed Nov. 7, 1963, Ser. No. 322,045 4 Claims. (Cl. 252-28) This invention relates to an improved lubricating composition and more particularly to a lubricant having the consistency of a grease suitable for high temperature lubrication.

The trend in design of modern aircraft has accentuated the need for a lubricant having the consistency of a grease which will lubricate anti-friction bearings operating at high rotational speeds and high temperatures. Considerable progress has been made in recent years in producing improved thickened lubricants for aircraft. For example, lubricating compositions having the consistency of a grease are now available for lubricating bearings operating at 10,000 to 20,000 revolutions per minute at temperatures up to about 400 F. However, great difiiculty has been encountered in producing a lubricating composition having the consistency of a grease which will effectively lubricate bearingsoperating at speeds of' 10,000 to 20,000 revolutions per minute and at temperatures up to about 600 F. for prolonged periods of time.

Since many of the lubricating characteristics of a thickened lubricant are imparted to the lubricant by the lubricating oil used in preparing the lubricant, a lubricating oil is required which is thermally stable at temperatures in the order of 600 F. While some lubricating compositions having the consistency of a grease have been prepared by thickening mineral lubricating oils, especially hydrotreated mineral lubricating oils, the volatility of mineral lubricating oils is such that as a general rule they do not give adequate lubrication at temperatures in the order of 600 F. over prolonged periods of time. Synthetic oils are substantially more resistant to thermal degradation than mineral oils. Synthetic oils, particularly the polyorgano siloxanes known as the silicone oils in addition to being more resistant to thermal degradation than mineral oils also have high viscosity indices making their use at high and ambient temperatures especially desirable. Thus, the lubricating oil employed in the composition of this invention is a synthetic lubricating oil.

Even though the synthetic lubricating oils have given improved lubricants, some difliculty has been encountered in producing a thickened synthetic lubricating oil which will give adequate lubrication of bearings operating at temperatures of 600 F. and speeds up to 20,000 revolutions per minute over a prolonged period of time.

We have discovered that a lubricating composition having improved lubricating characteristics for an extended period of time when used to lubricate bearings operating at temperatures up to about 600 F. and speeds of 10,000 to 20,000 revolutions per minute can be obtained by incorporating into a synthetic lubricating oil in oil thickening proportions malonoguanamine which prior to being incorporated into the oil has been heated to a temperature of about 450 to about 600 F. for a time sufiicient to reduce the weight of the malonoguanamine by about 20 to about 25 percent. Thus, the improved lubricating composition of our invention comprises a dispersion in a synthetic lubricating oil of a sufficient amount to thicken the lubricating oil to a grease consistency of heat-treated malonoguanamine.

The malonoguanamine which is heat-treated for use in the composition of the invention can be prepared by any known chemical procedure. Neither the compound per se nor its method of preparation constitutes any portion of the invention. Malonoguanamine has a melting point above about 360 C. and can be illustrated by the following structural formula, the circles within the six-membered rings indicating ring unsaturation.

After the malonoguanamine is heated to a temperature of about 450 to about 600 F. for a time sufficient to reduce its weight by about 20 to about 25 percent, the melting point of the heat-treated product is above about 450 C. The product is a dark brown powder. While we do not wish to be limited to any theory with respect to what happens while heat-treating the malonoguanamine, we believe that some polymerization takes place with the evolution of ammonia. The reduction in weight is equivalent to the splitting off of about 2.75 to about 3.5 moles of ammonia per mole of malonoguanamine. Regardless of the theory with respect to what happens during the heattreating step, we have found that heat-treated malonoguanamine when incorporated in a synthetic oil in an amount sufficient to give a composition having the consistency of a grease results in a composition having a performance life surprisingly above the performance life of a composition prepared from malonoguanamine which has not been heat-treated.

The malonoguanamine used in the composition of our invention is preferably heated at a temperature of at least 450 F. While lower temperatures can be employed, the time required to reduce the weight of the malonog-uanamine by about 20 to about 25 percent becomes commercially unattractive. Temperatures above about 600 F. can be employed, but, unless effective agitation is employed, the product may become charred or otherwise rendered less desirable for use as an oil-thickening agent. The time required to effect a 20 to 25 percent reduction in the weight of the malonoguanamine may vary from less than an hour to one hundred hours or more depending upon the efliciency or the heating method, the amount of malonoguanamine being treated and the degree of agitation during the heating. In any event, we prefer to employ a temperature of about 450 to about 600 F. with agitation to effect a 20 to 25 percent reduction in weight in a minimum amount of time.

The amount of heat-treated malonoguanamine which We use may vary depending upon the particular lubricating base employed and upon the characteristics desired in the ultimate composition. In any event, the amount of heat-treated malonoguanamine used in an amount sufficient to thicken the lubricating oil to a grease consistency. In general this amount comprises about 10 to about 40 percent by weight of the total composition.

The synthetic lubricating oil which is employed in the composition of the invention is selected from the group consisting of the liquid polyorgano siloxanes having a high phenyl content and diphenylmethylsilyl end groups and polyaryl ethers. The polyorgano siloxanes can be obtained by hdrolyzing and polymerizing a mixture of diphenylmethylchlorosilane, dimethyldichlorosilane and diphenyldichlorosilane preferably in a ratio of 1:1:1, respectively, according to procedures known to those familiar with the art. While the polyargano siloxanes are generally a mixture of polymers, a general formula representing the polymer mixture by an ideal molecule is as follows:

s 5 z l s s z s where x and y can be from 1 to 10 or more. An ideal molecule of a polyorgano siloxane having diphenylmethylsilyl end groups and a molecular weight of 954 is represented by the formula Exemplary of the polyaryl ethers which can be used are the polyphenyl ethers, i.e., m-bis(rn-phenoxyphenoxy)- benzene and tm-bis(m-phenoxyphenoxy)phenyl ether.

The lubricating composition of this invention can contain conventional lubricant additives, if desired, to improve other specific properties of the lubricant without departing from the scope of the invention. Thus, the lubricating composition can contain an auxiliary thickening agent, a filler, a corrosion and rust inhibitor, an extreme pressure agent, an anti-oxidant, a metal deactivator, a dye and the like. Whether or not such additives are employed and the amounts thereof depend to a large extent upon the severity of the conditions to which the composition is subjected and upon the stability of the synthetic lubricating oil base in the first instance. Since the polyorgano siloxanes, for example, are in general more stable than mineral oils, they require the addition of very little, if any, oxidation inhibitor. When such conventional additives are used they are [generally added in amounts between about 0.01 and about 5 percent by weight based on the weight of the total composition.

In those instances when an auxiliary thickening agent such as finely divided amorphous silica, bentom'te-organic base compound or esterified siliceous solid is employed, it is added in amounts of about 0.5 to about 3 percent by weight.

In compounding a composition of the present invention, various mixing and blending procedures may be used. According to one embodiment of the invention, the synthetic lubricating oil, the heat-treated malanoguanamine together with conventional lubricant additives, if desired, are mixed together at room temperature for a period of about to minutes to form a slurry. During this initial mixing period some thickening is evidenced. Some lumps may be formed. The slurry thus formed is then subjected to a conventional milling operation in a ball mill, a colloid mill, homogenizer or similar device used in compounding greases to give the desired degree of dispersion.

In order to illustrate the lubricating characteristics of a grease composition of the invention when used to lubricate bearings operating at 600 F. and at rotational speeds of 20,000 revolutions per minute, Pope spindles were used in a test procedure similar to that outlined by the Coordinating Research Council Tentative Draft (July 1954), Research Technique for the Determination of Performance Characteristics of Lubricating Grease in Antifriction Bearings at Elevated Temperatures, CRC Designation L-35. According to the CRC L test .method, the test bearings are packed with 3.5 cc. (or

equivalent weight) of grease. Because of the extremely short life of bearings packed with 3.5 cc. of grease, the present evaluations were made by packing the bearings completely full with about 6 to 8 grams of grease and using either a standard end cap with no additional grease or a special end cap holding a reservoir of about 10 grams of additional grease. The bearing assembly containing an eight-ball SAE No. 204 ball bearing is mounted on a horizontal spindle and is subjected to a radial load of 5 pounds. The portion of the spindle upon which the test bearing assembly is located is encased in a thermostatically controlled oven. By this means the temperature of the bearing can be maintained at a desired elevated temperature which in the tests reported hereinafter was 600 F. The spindle is driven by a constant belt-tension motor drive assembly, capable of giving spindle speeds of 20,000 revolutions per minute. The spindle is operated on a cycling schedule consisting of a series of periods, each period consisting of 20 hours running time and 4 hours shutdown time. The test continues until the lubricant fails. The lubricant is considered to have failed when any one of the following conditions occurs, (1) spindle input power increases to a value approximately 300 percent above the steady state condition at the test temperature; (2) an increase in temperature at the test bearing of 20 F. over'the test temperature during any portion of a cycle; or (3) the test bearing locks or the drive belt slips at the start or during the test cycle.

The lubricating oils used in preparing the lubricating compositions shown in Table I are synthetic oils known as QF-6-7024 Fluid and QF-6-7039 Fluid each of which is marketed by Dow-Corning Corporation. QF-6-7024 Fluid is considered to be a methylphenylsiloxane polymer wherein the end silicon atoms are substituted to a high degree by two phenyl groups and one methyl group. The material is highly resistant to radiation. QF-6-7024 Fluid has as typical characteristics a viscosity at 100 F. of about 930 to 1030 SUS, a viscosity at 210 F. of about to SUS, a viscosity index of about 108 to 110 and a pour point of +l0 to +20 F. It is believed that the types of side chains present and their approximate molar percentages (in brackets) in QF-6-7024 are phenyl [65], methyl attached through silicon to methyl [25] and methyl attached through silicon to phenyl [10]. An ideal molecule of a poly-organo siloxane having this analysis is as follows:

3 s s) z l 3 z l 2 s s z l 2 s 5)2 3 The oil known as QF-6-7039 Fluid is also considered to be a methylphenylsiloxane polymer inhibited against deterioration and otherwise similar to QF-6-7024 Fluid.

A typical procedure for preparing malonoguanamine and heat-treated malonoguanamine is as follows: Into a flask equipped with a stirrer and a distillate condenser are placed 640 m1. of ethylene glycol, 200 ml. of benzene and 32 grams (0.58 mole) of solid potassium hydroxide. The contents of the flask are then boiled with stirring to remove water as an azeotrope with benzene. When all the water is removed, the remaining benzene is removed by distillation. To the solution thus obtained are added 240 grams (2.86 moles) of dicyandiamide and a mixture of 52.8 grams (0.4 mole) of malononitrile in an equal volume of ethylene glycol, the latter mixture being added dropwise. The mixture is then heated to C. for a few minutes and thereafter cooled to 80 C. at which time 600 ml. of ethanol is added. The mixture is then poured into 600 ml. of water containing 10 ml. of concentrated hydrochloric acid. The mixture is then allowed to stand overnight. Thereafter, 50 ml. of ammonium hydroxide is added to the mixture with stirring and the product is filtered, washed with water and dried by heating at 110 C. The dried product, malonoguanamine, is a solid having a melting point above 360 C. Thirty grams of the malonoguanamine thus obtained are placed in an open beaker in an oven for sixty-six hours at 580 F. At the end of sixty-six hours, 23 grams of heat-treated malonoguanamine are recovered. The weight loss corresponds to a reduction of about 23.3 percent. The heattreated malonoguanamine has the appearance of powdered 'cotfee and a melting point above 450 C.

The Cab-O-Sil employed in preparing the compositions shown in Table I is a finely-divided amorphous silica marketed by Godfrey L. Cabot, 'Inc. This silica is a submicroscopic particulate silica prepared in a hot gaseous environment (1100 C.) by the vapor-phase hydrolysis of a silicon compound. On a moisure free basis, this silica is 99.0 to 99.7 percent silicon dioxide which is practically free from contaminating metallic salts. Gravimetric analyses fail to detect the presence of any calcium or magnesium. The iron content has been found to be about 0.004 percent and volatile matter removed on ignition at 1000 C. amounts to less than 1 percent. Cab- O-Sil is an extremely fine silica with particles ranging in size from 0.015 to 0.020 micron.

In preparing the illustrative lubricating compositions,

the oil, the malonoguanamine and the silica when used were mixed at room temperature for a period of to 30 minutes. The slurry thus formed was passed twice through a Premier colloid mill set at a stator-rotor clearance of 0.0015 inch. The approximate makeup and properties of thickened lubricating compositions of the invention thus prepared are set forth in Table I.

The long performance life of compositions'of the invention at a high rotational speed and a high temperature is self evident from the above data. When a composition was prepared by incorporating 38 grams of malonoguanamine which had not been heat-treated into 62 grams of QF-6-7024 Fluid according to procedure used in preparing Compositions A, B, and C, a performance life of only 1 6 hours was obtained at 20,000 and 600 F. The performance life obtained with the heat-treated malonoguanamine is thus almost tenfold that obtained with the malonoguanam-ine which has not been heattreated.

Other lubricating compositions within the scope of the invention are illustrated in Table The polyaryl ethers shown in Table :II have the following typical characteristics.

While our invention has been described with reference to various specific examples and embodiments, it will be understood that the invention is not limited to such examples and embodiments and may be variously practiced within the scope of the claims hereinafter made.

We claim:

1. A lubricating composition comprising a dispersion in a major amount of a synthetic lubricating oil selected from the group consisting of liquid polyorgano siloxanes having diphenylmethylsilyl end groups and polyaryl ethers of a suflicient amount to thicken the lubricating oil to a grease consistency of malonoguanamine which prior to being incorporated into the oil has been heated to a temperature of about 450 to about :600 tor a time sufiicient to reduce the weight of the malonoguanamine by about 20 to about 25 percent.

2. The lubricating composition of claim 1 wherein the heat-treated rnalonoguanamine comprises about 10 to about percent by weight of the total composition.

3. A lubricating composition comprising a dispersion in a major amount of a liquid poly-organo siloxane having diphenylmethylsilyl end groups of about 10 to about 40 percent by weight of malonoguanamine which prior to being incorporated into the liquid polyorgano siloxane has been heated to a temperature of about 450 to about 600 F. for a time suflicient to reduce the weight of the malonoguanamine by about 20 to about 25 percent and about 0.5 to about 3 percent by weight of finely-divided silica.

4. A lubricating composition comprising a dispersion in a major amount of a liquid polyphenyl ether of about 10 to about 40 percent by weight of malonoguanamine which prior to being incorporated into the liquid polyphenyl ether has been heated to a temperature of about 450 to about 600 for a time sufficient to reduce the weight of the malonoguanarnine by about 20 to about 25 percent and about 0.5 to about 3 percent by weight of finelydivide-d silica.

(1) (2) (3) 40 References Cited by the Examiner UNITED STATES PATENTS Viscosity, SUS

g2 8: E 2,427,315 9/ 1947 llhurston 260-249.9 P P t '13: +35 +4 2,984,624 5/1961 Halter 61', al. X

45 E1; rfii-l?ism-phenfixyphgrtoxy)benene. d DANIEL CE. W Y MAN, Prz mary Examiner.

2 is enoxyp enoxy enzene mixe isomers (3) Bis-iiflm-phenoxyphenoxy)phenyl ether. VAUGHN, Assistant Examiner- Table II Composition, Percent By Weight D E F G H Polyaryl Ether:

In-Bis(m-phenoxyphenoxy)benzene 87 Bis(phenoxyphenoxy)benzene (mixed isomers) 70 Bis-m(m-phenoxyphen0xy)pheny1 ether 60 Malonoguanamine (heat-treated) 30 40 10 19 .5 Cab-O-SiL-" 3 0.5 

1. A LUBRICATING COMPOSITION COMPRISING A DISPERSION IN A MAJOR AMOUNT OF A SYNTHETIC LUBRICATING OIL SELECTED FROM THE GROUP CONSISTING OF LIQUID POLYORGANO SILOXANES HAVING DIPHENYLMETHYLSILYL END GROUPS AND POLYARYL ETHERS OF A SUFFICIENT AMOUNT TO THICKEN THE LUBRICATING OIL TO A GREASE CONSISTENCY OF MALONOGUANAMINE WHICH PRIOR TO BEING INCORPORATED INTO THE OIL HAS BEEN HEATED TO A TEMPERATURE OF ABOUT 450* TO ABOUT 600*F. FOR A TIME SUFFICIENT TO REDUCE THE WEIGHT OF THE MALONOGUANAMINE BY ABOUT 20 TO ABOUT 25 PERCENT.
 3. A LUBRICATING COMPOSITION COMPRISING A DISPERSION IN A MAJOR AMOUNT OF A LIQUID POLYORFANO SILOXANE HAVING DIPHENYLMETHYLSILYL END GROUPS OF ABOUT 10 TO ABOUT 40 PERCENT BY WEIGHT OF MALONOGUANAMINE WHICH PRIOR TO BEING INCORPORATED INTO THE LIQUID POLYORGANO SILOXANE HAS BEEN HEATED TO A TEMPERATURE INTO THE LIQUID POLYORGANO SILOZ 600*F. FOR A TIME SUFFICIENT TO REDUCE THE WEIGHT OF THE MALONOGUANAMINE BY ABOUT 20 TO ABOUT 25 PERCENT AND ABOUT 0.54 TO ABOUT 3 PERCENT BY WEIGHT OF FINELY-DIVIDED SILICA. 